William Holloway

Imbibition of concentrated suspensions in capillaries

We observe the imbibition of concentrated suspensions of rigid spherical particles into capillary tubes. We find that while the meniscus position advances according to the square root of time, the pre-factor of this “diffusive” scaling is smaller than that predicted by an ad-hoc extension of classical imbibition using an effective viscosity for the imbibing fluid. The reduction in the pre-factor is traced to the presence of axial variations in particle volume fraction, which arise as a result of shear-induced migration of particles across streamlines. In addition, we develop a model that accounts for the effect of both radial and axial variations in particle volume fraction on the movement of the imbibition front which partially accounts for the main experimental observations.